Effects of delayed nitrogen fertilizer drip timing on soil total salt, cotton yield and nitrogen fertilizer use efficiency

Soil salinization in arid regions severely limits cotton growth by restricting nitrogen availability. Optimizing nitrogen application timing in conjunction with effective salt leaching is a potential strategy to enhance nitrogen uptake and improve yield. Therefore, this study aimed to evaluate the effects of nitrogen drip timing on soil salt leaching, available nitrogen distribution in the soil profile, and cotton yield. We conducted an indoor 15N labeled fertilizer leaching experiment and a two-year field experiment to adjust the nitrogen dripping time while applying the same amount of pure nitrogen. Specifically, “t” was defined as the total duration of one irrigation cycle, and the starting points for nitrogen application were as follows: T1, 1 h; T2, 1 h + 1/3 t h; T3, 1 h + 2/3 t h; CK, 1/3 t h and CK0 (no fertilization treatment). The results of indoor experiments revealed that the 15N abundance of the T3 treatment was the highest in the 0–20 cm soil layer, which was 57.50 % and 46.51 % higher than that of the T1 and T2 treatments. The results of field experiment show that T3 treatment significantly reduced the total soil salt, which was 25.49 % lower than that of T1 treatment at the bud stage. At the bud stages, the NO3- content of T3 treatment was 1.82 times higher than that of T1 treatment. In the boll opening stage, T3 treatment achieved the highest ammonium nitrogen content, which was 23.43 % higher than that of T1 treatment. At the flowering-boll stage, the nitrogen accumulation of T3 treatment was 30.17 % higher than that of CK treatment. The cotton yield was 11.63 % higher of T3 treatment compared to CK treatment. From the perspective of soil salinity, nitrogen distribution, nitrogen accumulation, and cotton yield, T3 treatment effectively removed salt and increased cotton yield.